It's Scrubbed

July 14, 2005|By Jeremy Manier Chicago Tribune

CAPE CANAVERAL, FLA. — Mystery: Engineers have battled problems with the pesky sensors on the external fuel tank since April.

In a disappointing setback for NASA's effort to return the space shuttle to flight, mission planners called off the launch of Discovery just hours before its scheduled liftoff Wednesday, citing a faulty fuel gauge in the vehicle's external tank.

Engineers could not immediately pinpoint the source of the glitch, which affected a sensor intended to shut down the spacecraft's engines if the fuel level gets too low. Mission planners said the earliest Discovery could fly would be Saturday afternoon, though the problem could set the flight back weeks or even months.

Shuttle engineers have struggled since April with the kind of sensor that caused trouble Wednesday. Two of the sensors malfunctioned during testing at that time -- a failure technicians never fully understood, though the glitch seemed to resolve itself after engineers replaced some circuitry on the orbiter.

The latest problem raised a new mystery. When flight controllers sent a signal that should have switched the four fuel sensors to a reading of "empty," one failed to respond.

"All I can say is shucks," said shuttle-program deputy manager Wayne Hale.

Launch director Mike Leinbach informed a disappointed crew that the launch would be scrubbed.

"I appreciate all we have been through together, but this one is not going to result in a launch attempt today," Leinbach told shuttle commander Eileen Collins, who was already strapped into the cockpit.

This is the second time NASA has had to cancel a planned Discovery launch date. In May, managers scrubbed a launch because of a separate issue with the external tank that required installation of a modified tank.

Asked if the failures are an embarrassment for NASA, Rep. Sherwood Boehlert, R-N.Y., said that, if anything, the delays are a good sign.

"Today constitutes a success," said Boehlert, chair of the U.S. House Committee on Science, which oversees NASA. "The success was the NASA team identifying a problem. Think about the alternative."

Shuttle engineers said that if the spacecraft were to fly without working fuel gauges, the engines might not shut off in the event that the tank ran out of hydrogen propellant sooner than expected.

That would result in the engines running dry -- something they were not designed to do.

The sensors "are there to protect us in case we run out of gas," Hale said. He said it took the shuttle managers about five minutes to decide that the faulty sensors meant the mission could not go forward.

Mission planners have not given up on the possibility that the problem could be resolved soon.

They said the astronauts will remain in Florida for the time being, and engineers will conserve energy in the shuttle's fuel cells so the spacecraft could launch in the next few days.

At several safety meetings, including a final one Tuesday, some NASA technicians had questioned whether the shuttle should fly at all until engineers understood what had caused the earlier fuel sensor problems.

"We had a long discussion during the prelaunch time period about how confident we were about the safety of flying with what we call an unexplained anomaly," Hale said.

But Hale said that at the last meeting the team decided unanimously it would be safe to fly the shuttle even without understanding the problem, because prelaunch tests would detect any malfunction.

That is exactly what came to pass, he said.

"You would really like to be able to say, 'This was it and I can prove it conclusively,"' Hale said. "But gosh, life's not like that all the time."

Some engineers also had said in preflight meetings that the shuttle should not fly without first running a "tanking test," a time-consuming effort that involves attaching the external tank to the shuttle. NASA performed such a test with the earlier external tank in April but decided not to do it again with the new tank.

"Since we don't know what the cause of this problem is, we don't know if it would have shown up in a tanking test," Hale said.

The sensor problem was magnified because of the intense pressure on the agency to revive the shuttle in the wake of the 2003 Columbia accident, in which seven astronauts lost their lives. But experts say launch delays are an unavoidable part of life in space travel.

Sen. Bill Nelson, D-Fla., who flew on the shuttle Columbia in 1986, pointed out that his mission was scrubbed four times before it finally launched. NASA director Griffin echoed Nelson's comments in minimizing the most recent glitch.

"I had one mission back in the '80s for the Defense Department that scrubbed 14 times before we finally got it off the pad," Griffin said. "This is nothing." *